Natural gas, referred to as green fuel, has emerged as a solution to depleting crude oil resources as well as to the deteriorating urban air quality problem. As a gaseous fuel, gains from natural gas have already been established in terms of low emissions of carbon monoxide, hydrocarbon and particulate matter. Air-fuel ratio, operating cylinder pressure, fuel injection, and compression ratio are some of the parameters that need to be analyzed and optimally exploited for better engine performance and reduced emissions. In this study, a comprehensive review of various operating parameters and concerns have been prepared for better understanding of operating conditions (spark and compression ignited engines) and constrains for a natural gas fueled internal combustion engine.